1. Field of the Invention
The present invention relates to the structure of a pulley of a belt driven continuously variable transmission and more particularly to a connecting structure between a moving sheave and a cylinder member or a piston member.
2. Prior Art
A belt driven continuously variable transmission comprises a primary (driving)shaft, a secondary (driven) shaft provided in parallel with the primary shaft, a primary pulley provided on the primary shaft, a secondary pulley provided on the secondary shaft and a drive belt looped over both of these pulleys, whereby the driving force is transmitted from the primary to the secondary pulley through the drive belt. The speed of the secondary shaft is varied continuously by changing a ratio of running diameters between both pulleys. The ratio of the running diameters is changed by regulating a groove width of both pulleys respectively.
As shown in FIG. 5, for example, a primary pulley 120 includes a fixed sheave 121 integrally formed with a primary shaft 130, a moving sheave 140 axially movable toward and away from the fixed sheave 130 on the primary shaft 121 and a hydraulic actuator 150.
The hydraulic actuator 150 includes a piston member 151 fixedly connected at one end thereof with the back surface of the moving sheave 140, a cylinder member 152 engaged at one end of thereof with the primary shaft 121 and a hydraulic oil pressure chamber 153 formed by the piston member 151 and the cylinder member 152.
The moving sheave 140 is moved by hydraulic pressure supplied to the oil pressure chamber 153, whereby a groove width L formed by the fixed sheave 130 and the moving sheave 140 is variably controlled.
Therefore, it is required that the piston member 151 is rigidly connected with the moving sheave 140 so as to secure a tight and pressure proof seal. According to an example of the prior art, this rigid connection is realized in such a way as shown in FIGS. 6a and 6b. FIG. 6a is a partly sectional view of the connecting portion of the piston member 151 and the moving sheave 140. A seal member, for example, a rubber seal member 145 is inserted into an annular groove 142 provided on a flange section 141 formed on the back surface of the moving sheave 140. After an end portion of the piston member 151 is fitted to the outer periphery surface of the flange section 141, the end portion of the piston member 151, as shown in FIG. 6b, is caulked into the annular groove 142 so as to rigidly connect the piston member 151 with moving sheave 140.
As an example of the prior art of connecting the piston member with the back surface of the moving sheave by caulking, there is Japanese Patent Application Laid-open No. Toku-Kai-Hei 9-217802. In this prior art, the moving sheave has a flange section with an annular groove on the back surface thereof and a steel wire is wound around the bottom surface of the annular groove. After the piston member is fitted to the flange section, an end portion of the piston member is caulked. According to the prior art, since the end portion of the piston member is subject to a plastic deformation by the steel wire, both side faces of the annular groove can have a firm contact with the piston member with a small amount of caulking.
On the other hand, Examined Japanese Patent Application No. Toku-Kou-Hei 4-79733 discloses a caulking technique in which the piston member is caulked into the moving sheave by pressing the end portion of the piston member with a roller, while the piston member is rotated integrally with the moving sheave.
Further, Japanese Patent Application Laid-open No. Toku-Kai-Hei 7-35211 discloses a technique in which the moving sheave is connected with the cylinder member by press-fitting an end of the cylinder member into the outer periphery of a boss of the moving sheave.
Also, there is a technique in which the moving sheave is connected at the outer periphery of a flange section thereof with the cylinder member by mean of a beam welding and the like.
However, in order to secure a firm connection with tight sealing all over the periphery of the flange section of the moving sheave, the caulking amount of the piston member and the dimensional tolerances of the annular groove must be precisely controlled. An inadequate control of the caulking amount causes a lack of strength in the connecting portion, cracks or deformation in the piston member. Further, the pressing load applied to the roller must be accurately controlled. If the pressing load is too large, cracks or constrictions are caused in the piston member, and thereby the strength of the piston member is lowered.
Further, in the connecting technique according to Toku-Kai-Hei 9-217802, winding a steel wire around the annular groove increases the manufacturing cost. Further, this technique requires a very precise control in the caulking amount to prevent cracks and constrictions from being caused in the piston member.
Further, the connecting technique according to Toku-Kai-Hei 7-35211 needs a press machine for press-fitting the cylinder member into the outer periphery of the moving sheave. In this case, also, a precise control of the press-fit amount is required so as to avoid the occurrence of cracks and the like. Further, in the case where the moving sheave is connected with the cylinder member by beam welding, a welding machine is needed and a means for avoiding the deformation of the cylinder member due to the thermal effect of welding is required.